Measurement of the shear strength of pure tungsten during one-dimensional shock loading

Abstract

The behavior of a pure tungsten under conditions of one-dimensional shock loading has been monitored using Manganin stress gauges, in longitudinal and lateral orientations. The shock induced equation of state, in terms of stress and particle velocity (from the longitudinal gauges), shows that the Hugoniot of this pure material agrees with the results of previous workers, both in pure tungsten and tungsten alloys. Lateral stress traces show an increase in stress (and hence decrease in shear strength) behind the shock front, in a manner similar to that observed in a tungsten heavy alloy and pure tantalum. It has been proposed that this is due to the high Peierl’s stress initially restricting dislocation generation, followed by a later increased in dislocation density. However, the brittle manner in which tungsten fails under shock loading indicates that other mechanisms are in operation. It has been suggested that the shock front nucleates cracking, which progressively grows behind it, which in combination with the proposed dislocation mechanisms reduces shear strength. Finally, we show that the variation of shear strength with shock stress is in agreement with a number of other workers until a stress level of ∼10GPa, where it is significantly higher. We have suggested that this is due to the higher strength of pure tungsten compared to the liquid phase sintered materials studied previously.